Rotary hammer tool



Nov. 5,1935. LRASCH 21,19,931

' I ROTARY HAMMER TOOL Fil ed March 22, 1955 2 Sheets-Sheet l zwl/enfar;

lwil/l'f fi f l Nov. 5, 1935. q 1.. RASCH 3 ROTARY HAMMER TOOL Filed March 22, 1955 2 Sheets-Sheet 2 2 2A 25 If:

I Mew/01 iizarwy Patented Nov. 's, 1935 UNITED STATES YP'ATENT OFFICE Applicationhiarch 22, 1935, Serial No. 12,506

Norway May 13, 1933 1 5 This invention relates to a rotary hammer,

' wherein a hammer body during the rotation of a ,carrying member is caused by centrifugal force to strike against a striking member or an anvil.

During its motion in the carrying member the hammer body is checked by an air cushionin a main" compartment arranged in the carrying member.. The cross sectional area of the main compartment is'substanti'ally fliled by the hammer body during its motion. The main compartment communicates with an auxiliary compartment which serves to regulate the checking action.

At any revolution of the carrying member the hammer is flung out from the main compart-- ment and strikes against the anvil. During further rotation of 'the carrying member the hammer again jumps into the main compartment, wherein its'velocity is braked or checked by an air cushion in the bottom of the main'compartment, the hammer being at the correct time pressed ahead again and gives oil a new blow. Thus at each revolution of the'carrying member one blow is eifected.

In hammers of this kind'an exact regulation of the braking efiect-is necessary, which depends upon the number or revolutions of the carrying member.

- against the compartmentbottom, becausein such case it might jump too early out from the comson theauxiliary compartment is used, whereby the size of the air cushion can never be reduced beyond the capacity of the auxiliary compartment. The operation of the air cushion is therefore softer, but frequently it is still too hard, so

that the hammer body jumps out too early.

Therefore, a pressure valve must be arranged which like a safety valve prevents the pressure in -the auxiliary compartment from increasing beyond a certain limit by letting out the superfluous air quantity. However, from this follows again an increased air vacuum during the motion -of the hammer body out from the main compartment. Besides, during this motion it should not be too much braked,v because then the intensity The hammer body should not strike.

of. the blow would be correspondingly reduced. Consequently, also a suction valve must be arrangedin order to let in air. Thus two valves were necessary in the carrying member, whereby the construction is complicated and the operation 5 unsafe. In addition, theescape of air through the pressure valve causes a considerable loss-in power. Further, the carrying member and the hammer body gradually become highly heated.

I have now discovered that the reason for the '10 said difliculties resides essentially in this that the main compartment and the auxiliary compartment have together a too small capacity. If this is increased, it may certainly be effected by increasing the auxiliary compartment. But 15 ;thereby their braking efiect during the last part of the inward motion of the hammer body will be too small, so that the hammer body is inclined to strike the bottom of the main compartment. Y

According to the present invention the said dlfllculties are avoided by having the connection between main and auxiliary compartments controlled by the hammer body proper.

In the previous constructions both compart- 25 ments were in open communication with one another, but according to the present invention this communication can be interrupted by the hammer body proper, when it has moved far enough into the main compartment and before 30 it has reached on to the bottom thereof. Only at the moment wherein the communication is interrupted,an eflicient air cushion arises in the bottom to stop the hammer body very rapidly close to its bottom "position. In this arrange- 35 ment the capacity of the auxiliary compartment may be considerably increased without a bottom blow be risked, The hammer body moves nevertheless always far into the compartment, and

air need not be let out. The air pressure behind 40 the hammer body will not, as before, increase evenly to the highest exhaust pressure, but it increases at first evenly and comparatively slowly until the said communication is interrupted. 5

Then the pressure increases very rapidly without any exhaust. During the hammer motion out from the compartment the pressure decreases correspondingly in the invert succession. The

braking is soft and only at the last moment hard.

An embodiment of the invention is illustrated in the drawings. Fig. 1 shows an elevation of the hammer partly in longitudinal section. Fig. 2 is a sectional view substantially on the line II-II of Fig. 1, the carrying member and the hammer to .located excentricaliy to the rotating axis 4 of the carrying member, and the hammer body turns during its return motion, after the blow against the anvil 5, into the'main compartment 6. However, it should never strike its bottom I. Nevertheless the hammer body should be caused to move most possibly close to the bottom. The carrying member 3 is maintained in rotation as usually in direction of the arrow by gear wheels 8, 9 from the motor shaft l0. Themotor is not shown. It is enclosed in a housing ll between the hammer housing l2 and the handle ii. The carrying member 3 is journalled in the housing l2 by means of ball bearings l4.

Now, according to my invention the auxiliary compartment i5 is separated from the main compartment 6 and communicates therewith through channels I6, ".18. The channel i8 ends in the lateral wall of the main compartment at some distance from the bottom face I and is closed as soon as the hammer body moves past it. As soon as the hammer body during its return rotation about the pivot 2 has reached the uttermost part I! of the main compartment, the braking commences. by the air contained in both compartments 6 and II. The braking effect increases softly and uniformly until the hammer body has closed thechannel l8. Then the air quantity behind the hammer body has been suddenly limited to a small air cushion within the compartment 6. Simultaneously the braking eifect increases very rapidly. The hammer body is stopped and againpressed out from the compartment, at first with a high force, whereby it is rapidly accelerated and then, as soon as the channel ID has been opened, with a less foree.-- In this manner an advantageous pressure curve is obtained.

Usually the air has no noticeable time to flow out from the compartments. But should this take place, a vacuum is created in the compartments. Such a vacuum also arises always in starting the tool. In order not to make the starting diflicult, a suction valve may according to my intention be arranged in the carrying member. The valve is provided with a lateral channel 20 enclosing a valve ball 2| with spring load 22. The channel 20 continues behind the valve seat into a lateral channel 23 ending in the compartment bottom I.

Provisions may also be taken to prevent the hammer body I from moving completely to the bottom of the compartment 6, when the hammer is to be stopped. For this purpose a side nose 24 is provided on a pin 25 movable radially in the carrying member 3, or other suitable means may be used. The pin is pressed by a spring 26 into the shown position, wherein the nose 24 projects into one corner of the compartment 6 so as to stop the inward motion of the hammer body, before it reaches the bottom I. When the hammer is started, the nose remains in this position, until the carrying member 3 has obtained a certain minimum number of revolutions. Then the centrifugal force pulls the pin 25 outwards'opposite the action of the spring 2, so that the nose 24 now is outside the compartment 6 and allows the hammer body tomove further in towards the bottom I.

The channel it ends in the auxiliary co'mpart ment l5 at or close to the point which is located most distant from the rotating axis 4. which might have entered the compartment IE will then always beremoved by the centrifugal force and pass out into the main compartment 6 with the expanded air.

I claim: v

1. A rotary hammer tool, comprising a rotary carrying member, a stationary surrounding casing, an anvil movably arranged therein, a

hammer body turnably mounted excentrically in said member, a main compartment so arranged in 20 the carrying member and so shaped that at one rotating direction the hammer body moves into the compartment in nearly tight proximity to its side walls opposed by an air cushion in the bottom part of the compartment and at the opposite 25 direction it moves, owing to centrifugal force, out from the compartment and produces a blow upon the anvil, a separate auxiliary compartment arranged in the carrying member, a communication passing from the auxiliary compartment to an 30 I opening arranged in the main compartment wall at some distance from its bottom, so that the hammer body during its motion in the carrying axis of the carrying member. 40 3. A rotary hammer tool according to claim 1,

wherein a loaded air suction valve is arranged in the carrying member and means connecting the suction side of the valve with the atmosphere and -the opposite side with the bottom of the main 45 compartment. 1

4. A rotary hammer tool according to claim 1, wherein a pin is arranged movably substantially radially in the carrying member, a spring tending to press said pin inwardly, a nose so arranged on 50 the pin that under the spring tension it is urged to project into the main compartment at some distance from its bottom.

5. A rotary hammer tool'according to claim 1,

wherein a pin is' arranged movably substantially 55 radially in the carrying membena spring'tending to press said pin inwardly, a nose so arranged on the pin that under the spring tension it is urged to project into the main compartment at some distance from its bottom, the spring being so sized m that the pin is retracted from the compartment by a predominant centrifugal force, as soon as the rotating velocity of the carrying member increases beyond a certain limit.

LUDVIK RASCH.

The oil 10 

